Against the background of a growing number of devices which are connected to local area networks, and a simultaneous increase in the data transmission rate in such local area networks, increased attention is being paid, firstly, to optimum-cost line routing and, secondly, to devices for ensuring that the signal quality is as high as possible.
One of the embodiments of local area networks that is used is the so-called Ethernet. The Ethernet is based on a serial databus with a number of devices (for example, data processing devices or communications terminals) which are connected to the databus and can at the same time each either receive or transmit data, with a device checking, before transmission access, that is to say the transmission of a so-called data packet, whether any data packets are currently being sent via the databus and, in situations in which this is the case, preventing transmission access by that device. As a result of the delay time effects that occur in relatively long databuses, it is possible for a situation to occur in which two devices are transmitting data packets simultaneously via the databus, thus resulting in the data packets associated with the different transmission devices colliding. This collision is generally identified by both transmitting devices, which then interrupt the transmission access and start again only after a time period which is chosen randomly by the devices.
Different types of coupling elements (referred to as node devices in the following text) are used for structuring a local area network, and the databus if the local area network is configured in the form of the Ethernet, into individual segments.
In the simplest case, a node device is in the form of a station, frequently referred to as a repeater in the literature, which receives data packets from a first segment of the databus, and passes them on to a second segment of the databus. This passing-on process is generally associated with signal regeneration, that is to say amplification and reshaping of the signal of the received data packets. Furthermore, electrical insulation and termination of the line are carried out between the connecting units of the node device, thus suppressing echo effects.
Differently configured node devices, frequently referred to as hubs in the literature, in contrast, allow a number of devices or else segments, to be linked in the form of a star to a databus. In a comparable way to a repeater, data packets (generally after comparable signal generation) are passed on identically to all the connections of the hub, and the connections are electrically insulated from one another and terminated.
When planning a local area network, active node devices generally have to be provided at regular intervals as the data transmission rate rises. Thus, the frequency of the data signals becomes higher, which compensates for any deterioration of the signal quality resulting from signal regeneration and termination of the signal-carrying lines.
An arrangement which allows the signal quality to be maintained in a local area network is distinguished, for example, by a large number of hubs which are each connected to one another via a short databus. Each hub, in this case, concentrates a number of devices connected to it at one node of the databus. This network design, which is frequently chosen for wiring at floor level in buildings, firstly has the advantage of small segmentations of a local area network and, thus, high signal quality. On the other hand, the resultant star-shaped topology has a disadvantageous effect on the complexity of the network wiring.
The present invention is directed toward specifying a node device which makes it possible to connect devices to a databus with little wiring complexity.